The present invention relates to inorganic reinforced polyamide resin compositions comprising crystalline polyamide resins, semi-aromatic amorphous polyamide resins, and inorganic reinforcing materials. More particularly, the present invention relates to inorganic reinforced polyamide resin compositions, which can provide shaped articles having satisfactory strength and rigidity without deteriorating their appearances (e.g, specular surface gloss, evenness of embossed surface) and further having excellent coating properties and weathering resistance, and which require a mold temperature of 100xc2x00 C. or lower in the preparation of shaped articles. These inorganic reinforced polyamide resin compositions are suitable for automobile exterior parts, particularly door mirror parts.
In general, polyamide resins have excellent mechanical characteristics, heat resistance, impact resistance, and chemical resistance; therefore they have been widely used for automobile parts, electrical appliance parts, electronic parts, domestic miscellaneous goods, and other various applications. Among these, polyamide resins reinforced with inorganic materials, typically glass fibers, have remarkably increased rigidity, strength, and heat resistance. In particular, it has been known that rigidity can be improved in proportion to the amounts of reinforcing materials added. However, if reinforcing materials such as glass fibers are added in large quantities, for example, in amounts of 50% to 70% by weight, to polyamide resins for the purpose of improving rigidity and strength, the polyamide resin compositions thus obtained provide shaped articles having extremely deteriorated appearance (e.g., specular surface gloss, evenness of embossed surface), resulting in a remarkable damage to the commercial value of these shaped articles.
Accordingly, for improving the appearances of shaped articles, there have been proposed many methods in which amorphous polyamide resins are added to crystalline polyamide resins (see, e.g., JP-A 2-140265, JP-A 3-9952, JP-A 3-269056, JP-A 4-202358).
These methods, however, cannot provide good specular surface gloss or even surface gloss of embossed surface. Further, there have been known methods for improving strength and rigidity by the addition of nylon-66, glass fibers, and mica in great amounts to semi-aromatic polyamide resins (MXD-6) (see, e.g., JP-A 1-263151). In this case, however, the temperature of a mold used in the preparation of shaped articles should be increased to high temperatures, for example, 135xc2x0 C., or even if the mold temperature is increased to such high temperatures, the shaped articles thus obtained may sometimes have no good appearances.
Under these circumstances, the present inventors have extensively studied to develop a polyamide resin composition, which can provide shaped articles having satisfactory strength and rigidity without deteriorating their appearances and further having excellent coating properties and weathering resistance, and which requires a mold temperature of 100xc2x0 C. or lower in the preparation of shaped articles, even if reinforcing materials such as glass fibers are added in large quantities, for example, in amounts of 50% by weight or higher, to polyamide resins for the purpose of improving strength and rigidity.
As a result, they have found that such a polyamide resin composition can be obtained by the combination of (A) a crystalline polyamide resin, (B) a semi-aromatic amorphous polyamide resin, and (C) an inorganic reinforcing material, and by the control of relative viscosity and crystallization temperature as measured with a temperature drop, of the composition after melt kneading of these ingredients, thereby completing the present invention.
Thus the present invention provides an inorganic reinforced polyamide resin composition obtainable by melt kneading of (A) a crystalline polyamide resin, (B) a semi-aromatic amorphous polyamide resin, and (C) an inorganic reinforcing material, wherein the relative viscosity of 96% sulfuric acid solution of the composition is 2.1 or lower and wherein the crystallization temperature (TC2) of the composition as measured with a temperature drop by differential scanning calorimetry (DSC) is 180xc2x0 C. or lower.